Ments



J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 27. 1922 3Sheets-Sheet ImrEn ar JnhnE E' ard nsr J. E. GARDNER AUTOMATIC TELEPHONESYSTEM Dec. 6, 1932.

Original Filed Jan. 27. 192 2 S'Shets-Sheet J. E. GARDNER 7 Dec, 6,1932, AUTOMATIC TELEPHON E -SYSTEM 7 Re. 18,686

-Origipal Filed Jaxi. 27. 1922 3 Sheets-Sheet 3 1m Jzhn EE-arcfnerReissuecl Dec. 6, 1932 UNITED STATES PATENT OFFICE I JOHN E. GARDNER, OFCLARENDON HILLS, ILLINOIS, ASSIGNOR, BY MESNE ASSIGN- MENTS, T0ASSOCIATED ELECTRIC LABORATORIES, INC., OF CHICAGO, ILLINOIS,

A CORPORATION OF DELAWARE AUTOMATIC TELEPHONE SYSTEM Original No.1,727,592, dated September December 3, 1928. Application for reissue Thepresent invention relates in general to automatic telephone systems, butis more particularly concerned with small exchanges of the type whichare commonly used for giving telephone service in factories, commerciales- 'tablishments and the like; and the object of the invention, broadlystated, is the provision of a private automatic exchange systemembodying new features and novel circuit arrangements which are betteradapted to meet the service requirements of systemsoftliis character.

According to the invention an attendant operator is employed at theprivate automatic exchange to complete all connections from the main tothe branch exchange. All connections in the other direction from theprivate automatic to the main exchange are completed automaticallythoughif need be the operator may complete the connection.

A feature of the invention relates to the provision of an improved largecapacity connector switch which has access to trunk lines extending toprivate automatic exchanges.

Another feature of the invention concerns itself with the provision of anovel trunk circuit extending from the main to the branch exchange sothat if a trunk becomes open or grounded it is automatically made busyin both exchanges.

A further feature of the invention relates to the provision of a novelcord circuit at the attendant operators position provided with improvedmeans for giving supervision.

Still another feature of the invention provides means for automaticallyrendering the trunk line accessible in either the main or branchexchange for a call in either direction when the calling subscriber atthe main exchange replaces his receiver, notwithstanding that theoperator may have the plug of a cord circuit in the associated jack.

Other features of the invention relate to the provision of means wherebywhen a call is extended from the main to a branch exchange subscriberthrough an operators cord circuit at the branch exchange the replacementof the receiver at the called substation causes the release of theconnection both in the main and branch exchanges and renders the trunk10, 1929, Serial No. 532,159, filed January 27, 1922. Renewed filedAugnstlz, 1931. Serial No. 556,698.

line connecting these exchanges accessible for calls in either directionand to the novel arrangement whereby when a connection is extended bythe operator in the branch exchange to a subscriber in the main exchangethe replacement of the receiver at the called substation in the mainexchange causes the release of the connection and the trunk line fromthe main to the branch exchange is rendered accessible for calls ineither direction even though the attendant operators cord circuitremains in the jack associated with this trunk line. 7

There are other objects of the invention not now specifically mentionedwhich together with the foregoing will be described fully hereinafterreference being had to the accompanying drawings forming a part of thisspecification. Referring now to the drawings comprising Figs. 1, 2, and3, there is shown by means of the conventional circuit diagrams enoughof the apparatus to fullyillustrate the invention. This apparatusincludes a large capacity rotary connector switch H, Fig. 1, in the mainexchange, atrunk line comprising conductors 140 and 141 extending to theprivate automatic exchange, a cord circuit 0, Fig. 2, a connector switchH, Fig. 3, and a subscribers station A in the private branch exchange.

Referring now more particularly to Fig. 1, the connector switch H is ofthe same general mechanical construction as that of the well knownStrowger switches, but differs from them inasmuch as it is provided withan extra set of wipers and associated bank contacts; thus the connectorH, which has twenty levels, has access to 200 lines and is capable oftesting, after selecting a group of lines, for an idle line in twolevels simultaneously. One of the trunk lines extending to a privateautomatic exchange to which the connector switch H has access is shownin the drawings terminating in the bank contacts 106-108, inclusive.

This trunk line is of the two way type, that is, it is adapted to beused for calls from the main to the branch exchange or from the branchto the main exchange. In order to The trunk line comprising conductors140 and 141 terminates in the jack J, Fig. 2, in

' the private automatic exchange. This trunk line also terminates inmultiple bank contacts in the outgoing levels of the local connectorswitches. This arrangement is not shown in the drawings but is wellknown and need not be described, it being sufiicient to say that theconductors 169171, inclusive, associated with the trunk line comprisingconductors 140 and 141 extend to the local connector selector repeaterswitches and are multipled therein in the usual manner.

At 0, Fig. 2, is shown a cord circuit at the attendant operatorsposition in the private automatic exchange. This cord circuit is one ofa plurality located at the attendant operators position which is usedfor extending incoming calls from a main exchange to a branch exchangesubscriber.

' The jack J is the terminal of a trunk line extending to an incomingconnector switch which is shown at H, Fig. 3.

The connector H is of the usual Strowger type having access to localsubscribe'rs lines such as that of the substation A.

The substation A is of the well known automatic type having the usualtalking instrumentalities and impulse sending device, the associatedline of which terminates at thelexchange in the line switch C.

The line switch C is similar to the line switch C, Fig. 1, alreadydescribed.

Having briefly described the apparatus shown in the drawings a detaileddescription of its operation will now be given. For this purpose it willbe assumed that a. subscriber in the main exchange desires to extend aconnection to a subscriber A in the private automatic exchange. It willbe assumed further that the subscriber in the main exchange has removedhis receiver and operated his calling device in order to cause theoperation of his individual line switch and the necessary t number ofselector switches in the main exchange to extend the connection to thetrunk line terminating in the connector H, Fig. 1, and comprisingconductors 1012, inclusive.

As soon as the connection is extended to the connector H the line relay16 thereof is energized over the two sides of the calling subscribersline in series and, upon operating, closes the circuit of its associatedslow acting relay 17. Relay 17, upon energizing, at its armature 37places ground upon conductor' 51 in the connector H in order to providea locking circuit for certain relays which become operated subsequently,at its armat'ure 39 opens a point in the circuit of the release magnet102, at the front contact of this armature prepares the impulsingcircuits of the connector H and at armature 38 places ground upon therelease trunk conductor 11 thereby establishing in the usual manner aholding circuit for the previously operated switches.

The calling subscriber may now operate his calling device for the nextdigit of the desired'number thereby producing a series of interruptionsin the circuit of the line relay 16 which retracts its armature aplurality of times in response thereto. At the first retraction of itsarmature an impulse of current is sent over a circuit extending fromground by way of armature 52 and its back contact armature 39 and itsfront contact, 0E normal' springs 41 and 40, through the winding of theslow acting low resistance relay 18, and thence through the winding ofthe vertical magnet 101 to battery. The above is the circuit over whichthe first impulse to the vertical magnet is transmitted. However, uponthe first vertical step of the switch the: off

normal springs are shifted and the remaining vertical magnet impulsestraverse a different circuit which is the same as the one previouslytraced except that it includes the off normal springs 41 and 42 andarmature 43 and its front contact, relay 18 being now in an operatedposition. The vertical magnet 101 operates to raise the switch shaftcarrying the two sets of wipers 103-105, inclusive, and 109-111,inclusive, step by step until these wipers stand opposite the levels ofbank contacts corresponding to the digit dialled. The slow acting relay18 is energized in series with the vertical magnet, maintains itsarmature attracted throughout the vertical operation of the switch andat the termination thereof deenergizes thereby transferring theimpulsing circuit to the rotary magnet 98.

The calling subscriber, upon operating his calling device for the nextand final digit of the desired number, causes the line relay 16 toretract its armature a number of times corresponding to the digitdialled. At each retraction of its armature 52 an impulse of current issent over the following path: from ground through the said armature andits back contact, armature 39 and its front contact, oif normal springs41 and 42, armature A 43 and its back contact, back contact and armature66, through the winding of the slow acting relay 27, armature 91 and itsback contact, and through the winding of the rotary magnet 98 tobattery. The rotary magnet 98 operates to rotate the switch shaftcarrying the two sets of wipers into engagement with the proper sets ofbank contacts in which terminate the first two trunk lines extending tothe desired private automatic exchange which we will'assume are the bankcontacts 106-108, inclusive, and 1124-14, inclusive. The slow actingrelay 27is energized in series with the rotary magnet and at itsarmature 72. closes the circuit of-the slow acting relay- 29, at itsarmature 71 short circuits the arma-' ture 66 and its back contacts onthe busy test relay 26 so as to prevent the rotary magnet circuit beinginterrupted by a premature energization of relay 26 while the switchwipers are rotating over busy contacts, and at its armature69'and 70opens certain points in the automatic rotary testing c rcuit whichwill'be described fully later. The slow actingrelay-29, upon operating,at its armature 80 closes thecircuitof the slow acting relay 28, at itsarmature!- 9 opens a point in the circuit of the upper winding ofswitching relay 30, atthe front contact of this armature connects thetest wiper 104E associated with the upper set of'bank contacts to thetest relay 26, at its armature 78 opens a point inthe circuit of relay20 and at its armature 77' prepares a point in the testing circuit of,the test wiper 110 associated with the second set of wipers. The relay28, upon energiz ing, at its armature 76 opens a point in the busysignallin circuit, at its armature 73 opens apo'nt in a circuit of relay20 and at its armatures Hand 75 prepares points in the automatic rotarytesting circuits.

At this point it will be convenient to explain howthe lines of a groupare connected in the bankcontacts of" the rotary connector switches soas'to enable these switches to selectidletrunk lines in the group afterhaving connected therewith. On all lines over which it is desired thatthe connector switchrotate iffthe line is busy the connection of thenormal conductors extending from the line switch to the connectorbanksare reversed. This may be seen by referring to the connection ofthe'normal conductors extend'ng from the line switch C to the bankcontacts 106108, inclusive. That is the conductor 141 which extends fromgroundlin the line switch C is connected to bank contact 106 instead ofbank contact 108 and the conductor 140 which is connected to battery inthe line switch G extends to contact 108 instead of contact 106. Theline switches associated with all the lines which are the end of thegroup in the rotary connector are changed so that a resistance appearsin-the private normal conductor as may be seen with reference to theline switch G, that is the connection between the term' nals 135 and 136which normally short circuits the resistance R and also the connectionwhich normally short circuits the resistance R are removed. Theseresistances are of'about300 ohms each and are included in the circuit sothat should this line be a call ground will appear on the private normalconductorthrough this resistance and if making a rotary connector switchis rotated into engagement with the bank contacts associated with thisline the rotation of the switch will cease and a busy tone will be givento the calling subscriber.

Adverting now to the operation of the connector H when engagement wasmade with the bank contacts 106408, inclusive, it will be assumed thatthe first trunk line of the group which is the trunk line now associatedwith the first set of wipers 103 105, inclusive, is busy there will be aground potential on the test contact 107 and the test relay 26 will beenergized over the following circuit :Grounded, test contact 107, testwiper i, armature 79 and its front contact, armature 90 and its backcontact, and thence through the winding of the test relay 26' tobattery. Relay 26, upon energizing, at its armature 65 prepares a pointin its locking circuit which is estab lfshed immediately upon thecleen-ergization of the slow acting relay 29, at armature 66 opens apoint in the circuit of th rotary magnet, at armature 67 prepares apoint in the circuit of switching relay 31, at armature 68 prepares apoint in the busy signalling lead, at its armature 64 switches theconnection of the test relay from the first set of wipers to the secondset for a purpose which will appear later and at its armature 63 closesa point in the circuit of the test relay 25. Assuming that the secondtrunk line of the group is busy a ground potential will be present onthe test contact 113. A circuit for the testing relay may now be tracedfrom grounded test contact 113, test wiper 110, armature 77, and itsfront contact, armature 63 and its front contact and through the windingof relay 25 to battery. Relay 25, upon energizing, at its armature 59prepares a point in its locking circuit which is completed immediatelyupon the deenergization of the slow acting relay 29, at its armature 62opens a point in the circuit of switching relay 31, at armature 28-2transfers the circuit of the slow acting relay 17 to ground at armature283 for a purpose which will be explained later, and at armatures and 61closes two points in the automatic rotary testing circuit. Immediatelyupon the deenergization of the slow acting relay 27, a circuit for theboth windings of the stepping relay 21 may be traced, the circuit ofwinding 24 extending contact 107, test wiper 104, armature and its frontcontact, armature 70 and its back contact, armature 61 and armature andits back contact, through the winding of the coil 24 and the resi tanceR to battery, and the circuit of winding 23 extending from grounded testcontact 113, test wiper 110, armature 74 and its front contact, armature69 and its back contact, armature 60 and its front contact, armature 99and its back contact and through the winding of the coil 23 andresistance R to battery. The

from grounded test.

its front contact, 3

relay 21 is energized over this circuit and,

upon operating, at its armatures 56 and 57 establishes locking circuitsfor both its windings 23 and 24, at armature 58 cioses the circuit ofthe rotary magnet 98. Magnet 98 operates to rotate the switch shaftcarrying the two sets of switch wipers into engagement with the next twosets of bank contacts and at its armatures 99 and 100 opens the circuitsof thecoils 23 and 24: of the stepping relay 21. Relay 21 deenergizesthereby opening the energizing circuit of the rotary magnet whichdeenergizes also. It will be noted that when an impulse of current issent to the rotary magnet 98 the slow acting relay29 wiil receive animpulse of current. Therefore, the slow acting relays 29 and 28 willremain on ergized to preserve the continuity of the testing circuits.

At this point it is convenient to describe the operation andconstruction of the stepping relay 21. Belay 21 is a relay of the socalled shunt field type, that is, it does not attract its armature withonly one coil energized as the relay armature is short circuited by thesoft iron core of the other coil. However, it will be apparent that whenboth coils 23 and 24 are energized magnetic flux must flow in a pathwhich includes the relay armature which will thus be attracted. Thewindings 23 and 24 of the coil 21 are of very low resistance (about 5ohms) and are in series with resistance coil R which is of somewhathigher resistance (about 50 ohms). The relay is wound in this manner sothat if there happens to be a ground potential upon the test contactsthrough a fairly high resistance say of about 300 ohms, which is thecase when the connector Wipers engage a busy line which is the lasttrunk line of the group, it will not.

be energized. That is, the relay, 21 does not attract its armature withone coil energized by a test contact which is directly grounded and theother coil is energized over a circuit which includes a test Contactgrounded through a resistance of about 300 ohms. It will be observedthat under these conditions the winding of the coil energized through300 ohms is practically short circuited by direct ground through one ofthe low resistance There is practically no margin to the adjustment oftherelay 21 inasmuch as under these conditions which are the mostadverse encountered the coil energized through 300 ohms generatespractically no magnetic flux and the flux generated by the other coil isshort circuited from the relay armature so that it does not operate.

Returning now to the trunk selecting operation of the connector switchH, if the next two trunk lines, which are now associated with both setsof wipers, are rotary trunks and busy, the relays 25 and 26 will bemain; tained energized and the stepping relay2l will again operate toclose the circuit of the rotary magnet 98 The alternate operation of thestepping relay 21 and the rotary magnet 98 continues until the switchwipers are rotated into engagement with anidle trunk line or a busytrunk line which is the last one of a group. It will be noted that eachimpulse sent to the rotary magnet 98 also keeps the slow acting relay 29energized so that the test wipers are maintained connected to theirrespective testing relays. V

Assuming that the upper set of wipers engage atrunk line which is thelast of a group ground will be connected to the test contact engaged bythe test wiper 104 through a resistance of 300 ohms. This resistancebeing included in the private normal circuit as will appear fully later.Relay 26 will be maintained energized by the stepping relay 21 will notoperate for the reasons stated above and the rotation of the connectorswitch will cease. The slow acting relays 28 and 29 deenergize and abusy tone is given to the calling subscriber over a circuit extendingfrom the busy machine. back contact and armature 76, front contact andarmature 68 to the lower line conductor 12 and thence over the callingsubscribers line. Upon hearing this signal the calling subscriber willreplace his receiver thereby initiating the release of the operatedswitches including the connector H in a manner which will be describedsubsequently. lVhere the last trunk line of the group terminates in aset of bank contacts engaged by the upper set of wipers 103105,inclusive, it is necessary to leave the bank contacts associated withthe lower set of wipers open and to ground the test contact of this setin order to secure proper operation of the connector H. However, wherethere are an even number of trunk lines in the group the last trunk linewill terminate in a set of contacts accessible to the lower set ofwipers and in this case no special provision is necessary. That is, itis unnecessary to leave any set of bank contacts disconnected from atrunk line. In order to describe the operation in this case it will'beassumed that the connector H rotates its wipers 109111, inclusive, intoengagement with the trunk line which is the last of a group. Theoperation in this case is similar to that above described, that is, therelay 26 remains energized as does the relay 25, the relay 21 remaininginoperative. As relay 21 does not energize the rotation of the switchceases and a busy signal is given to the calling subscriber.

It will now be assumed that the connector H is rotated until its upperset of wipers are associated with an idle trunk line in the group. Underthese conditions there will be no ground potential present upon the testcontact engaged by the test wiper 104. Relay 26 deenergizes and opensthe circuit of the testrelay 25. Then immediately upon thedeenergization of the slow acting relay 29 a ;.armature 96, back contactand armature 79,

test wiper 104, test contact associated with it, and thence over theprivate normal conductor thereof through the winding of the switchingrelay in the associated line switch and motor magnet to battery. Therelay 80 is energized over this circuit, and upon operating, establishesa locking circuit for itself at its armature 88, opens a point in thecircuit of the testing relay 26 at armature 90, opens the rotary magnetcircuit at armature 91, at armature 89 places direct ground upon thetest Wiper 104;, at armature 87 prepares a circuit for giving thecalling subscriber the so called ringing induction and at armatures 86and 92 completes the ringing circuit. Ringing current is now projectedout on the trunk line until a response is obta ned. Other results of theenergization of relay 80 are that-at armature 283 ground is removed fromarmature 3284 for a purpose which will be described,

and at armature 285 a locking circuit is prepared for the relay 25.

The above is the operation of the connector H when an idle rotary lineis connected with. However, if the idle line engaged by the upper set ofwipers is the last trunk line in the group the operation is slightlydifferent. This will now be briefly described. It will be noted thatupon the deenergization of the slow act- 'ing relay 29, when a circuitis completed for the switching relay 30, a circuit is prepared whichextends from battery through the winding of relay 20, normally closedsprings cont-rolled by armature 18, armature 6 1 and its back contact,armature 7 8 and its back contact, back contact and armature 92,armature 97 and its back contact, to wiper 105. It has been describedbefore how the normal conductors extending from the line switch arereversed in case the line is a rotary line and how if the line isstraight they are connected in the usual manner. As it is assumed thatthe upper set of wipers are now in engagement with a trunk line which isthe last of the group there will be ground on the bank contact engagedby the wiper 105 from the back contact of an armature in the associatedline switch such as the armature 129 in the line switch (I. The relay istherefore energized, and upon operating, at its armature 18 establishesa locking circuit for itself, at its arina ture 4C9 removes directground from the armature 89 on the switching relay and at its armatures17 and reverses the connections between the wipers of the connector andthe connections to the ring cutoff and back bridge relays 19 and 15,respectively. Upon the energzatiou of the switching relay 30 whichocours in the same manner as before described, ground'is placed upon thetest contact engaged by the test wiper 104, through the resistance Rwhich is of about 300 ohms. The other circuit changes brought about bythe energization of the switching relay 30 are the same as beforedescribed except that ringing current is now sent over the wipers of theconnector H in the opposite direction. This is for a purpose which willappear fully later.

Should the lower set of wipers of the connector H have been the first toengage an idle trunk line the operation of the connector differs fromthat above described in the following manner The test relay 26associated with the upper set of wipers remains energized while the testrelay 25 deenergizes; Under these conditions the rotation of the switchis stopped and immediately upon the deenergization of the slow actingrelay 28 a circuit is completed extending from ground byway of frontcontact and armature 67, armature 62 and its back contact, through theupper winding of the switching relay 31, back contact and armature 74,test wiper 110 associated with the lower set of wipers, test contactengaged thereby and thence over the private normal conductor through theswitching relay and motor magnet of the associated line switch tobattery. The switching relay 31 is energized over this circuit and, uponoperating, establishes a locking circuit for itself at armature 94, atthis same armature closes a circuit for the lower winding of theswitching relay 30 at armature places ground upon the test contactengaged by the test wiper 110, at armature 96 opens a point in thecircuit of the upper winding of relay 30 and at armature 93 and 97disconnects the first set of wipers and connects up the second set. Theenergization of the switching relay 30 produces the same results asbefore except that ground is disconnected from the armature 89 so thatthe wiper 104 will remain disconnected from the switch. In the aboveoperation, upon the deenergization of the slow acting relay 28 thediscriminating relay 20 is connected with the wiper 111 of the lower setof wipers in order to test whether or notthe associated line is the lastone of a group. If the associated line is the last one of a group, relay20 is energized and operates as before described, that is, upon theenergization of the switching relays 30 ant. 31 ringing current will beprojected in the opposite direction from the wipers of the connector andground will be supplied by the test contact engaged by the test wiperthrough the resistance R so that if another connector is rotatedinto'engagement with this limits rotation will be stopped and a signalgiven to the calling subscriber.

Returning now to the description of the extension of the connection itwill be assumed that when the connector H was operated into engagementwith the bank contacts 106-108,

M an inclusive, the associated line was idle. Under these conditions therelay 26 is not energized and immediately following the deenergizationof the slow' acting relay 29 the discriminating relay 20 isconnected tothe wiper 105 at armature 78 and the circuit of the switching relay 30is closed at armature 79.

As the bank contacts 106-108, inclusive, areassociated with the firstline of a group eX- tending to the private automatic exchange theconnector switch must rotate over it when it is busy and therefore, thenormal conductors will be connected in the reverse manner and thediscriminating relay 20 will not be energized as the contact 108 isconnected to battery in the line switch C. Switching relay 30 isenergized over the following circuit: ground on release trunk conductor11', armature 65 and its back'contact, through the upper winding ofswitching relay 30, back contact and armature 96, back contact and armature 79, test wiper 104, test contact 107, through the winding of theswitching relay 121 and the motor magnet 125 of the line switch C tobattery. Relay 121 is energized over this circuit. However, itsoperation at this time is only effective to open its back con.- tactsbut not to close its working contacts on account of a mechanicalinterlocking device controlled by the armature of the line relay 123which is now normal. The operation of relay 121 disconnects the normalbattery and ground connections in the line switch C from the trunkconductors 140 and 141.

In theconnector H relay 30, upon operating, makes certain circuitchanges ina manner which has already been described. these being amongothers: Ground is placed upon the test contactlO'Z' and the ringingcircuit is closed. Ringing current is now intermittently projected overthe trunk line comprising conductors 140 and 141 extending to theprivate automatic exchange. It will be noted that ringing current leavesthe wiper 103 and returns to the wiper 105. The operation. of the relay121 in" the line switch (has before stated, removes the normal batteryconnection from the trunk line comprising conductors 140 and 141. Sincethe conductors 140 and 141 are reversed in the bank contacts of theconnector H the battery supplied by the connector H superimposed on theringing current is of the opposite polarity to that normally supplied bythe line switch C when the trunk line is not in use. The relay 152 inthe trunk circuit associated with this trunk line at the privateautomatic exchange is a high resistance polarized relay normallyenergized by battery on the trunk in series with the windings of theline relay 123 and the relay 122 and consequently it will retract itsarmature 165 whenever battery is removed from the trunk or reversedthereoverl Thus as soon as the trunk line is seized by the connectorHthe relay 152 will retract its armature.

Upon deenergizing, relay 152 completes a circuit extending from groundby way of back contact and armature 162, armature 165 and its restingcontacts and thence through the winding of the slow acting relay 153 tobattery. Upon energizing, this latter relay at armature 167 placesground upon the release trunk conductor 170 extending to multiple testcontacts associated with this trunk line in the outgoing level of thelocal connector switches thereby making this trunk line busy to anyoutgoing calls and at armature 173 prepares a point in its lockingcircuit. The relay 150 in this trunk circuit is bridged across theconductors 140 and 141 in series with a condenser and is operated by theringing current from the connector H. Relay 150, upon energizing,establishes a locking circuit for itself at its armature 161 and at itsarmature 160 closes the circuit of the line lamp L. Upon noting thissignal, the attendant operator will, insert the plug of an idle cordcircuit, which we will assume is the plug P ofthe cord circuit 0, intothe jack J. By

this operation a circuit is completed extending from ground through thewinding of the low resistance relay 175, normally closed springscontrolled by armature 181, sleeve of plug P, sleeve of jack J andthrough the winding of relay 151 to battery. The relays 175 and 151 areenergized over this circuit. Relay 151. upon operating, at its armature163 opens the locking circuit of the ring up rclay 150, at its armature164 removes the polarized relay 152 as well as the lower winding of thering up relay 150 from bridge of the trunk conductors 140 and 141 and atits armature 162 removes one ground connection from the armature 165 ofthe polarized relay. This latter operation is ineffective at the presenttime as ground has been connected to the armature 165 by the operationof spring 155 of ack J. The visual signal 168 is energized in multiplewith relay 151. However, its operation is without function at thepresent time. In the cord circuit 0, relay 175 at its armature 180closes the circuit of the polarizing winding of the electropolarizedrelay 17 7 and also the circuits for the supervisorylamps L and L Itwill be noted that the lower winding of the polarized relay 177 isbridged directly across the cord circuit and consequently across thetrunk line comprising con-' ductors 140 and 141. The ring out off relay19 in the connector H is therefore energized in series with the lowerwinding of relay 177. Upon operating, relay 19 establishes a lookingcircuit for itself at armature 45, at armatures 44 and 46 opens theringing circuit and at the front contacts of these armatures con-' nectsup the back bridge relay 15. Back bridge relay 15 is also energized overthe trunk line. and upon operating, reverses the normal current flowover the incoming trunk lines comprising conductors 10 and 12 forsupervisory or metering purposes. Another result of the energizationofrelay isthat a circuitis closedat armature 32 for the slow actingrelay 83. Upon operating, the latter relay at armature l prepares acircuit for the relay in order toprepare a releasecircuit for theconnector which will be explained hereinafter. In the cordcircuit-Qtheelectropolarized relay 177 is energized in'series with thering out 01f relay 19 as the current flow from the connector -H is inthe proper direction to operate it. Upon operating, relay 177 at itsarmature 186 opens the circuit of thesupervisony lamp L and at itsarmature 187 closes the circuit of the slowacting relay 178. Relay 178,upon'operating, prepares acircuit for the relay 1'7 6 at armature 188.The attendant operator will now throw the listening key K therebyassociating her head set with the cord circuit and enabling hertoascertain whatnumberthe calling subscriber in the main exchange desires.Should theattendant operator plug into the jack J with the listening keyK thrown'she .would likely get a ringin-the ear-were not specialprovisions made'to prevent this. If ringing current is being impressedon the trunkline when the operator plugs .in the jack J with the key Koperated the alternating current relay 192 associated with her head setwould be energized. Upon operating, relay 192 at armature 193 shortcircuits the right hand Winding of the repeating coil through the resis'rance 1%. This prevents any disagreeable noises in the operatorsheadset dueithe ringing current. l/Vhen theattendant operator finds outwhat number .is desired shewill insert the plug P into an idle jackwhichwe Will assume is the jack Jextendingt-o themcoming connector switch H,Fig. 3. By this operation a circuit-is completed'for the line relay2100f the connector H over .the following path: fromground by way ofnormally closed springs controlled by armature 191, impulse springsofthe calling device' CD, springs of the release key K spring 196 andits working Contact, sleeve of plugPQsleeve of jack J,-springs 198 and199, conductor .201 and through the winding of theline relay21O ofthecontactor H to battery.

The relay 210 is energized over this circuit and, upon operating, closesthe circuit for its associated slow acting release relay 211. Uponoperating, the latter relay opens the L release magnet circuit atarmaturea229, at the front contact of this armature preparestheoperating circuits of the connector H and at armatures 227 and 228prepares certaincircuits for other relays in the switch.

It will benoted that the line relay 210 is not connected directly to thesleeve of thejack J but is connected through the springs 198 and 199.The connection is made in this manner so that there will be-no socalledpreliminary impulse sent to theline relay 210 due to acontactbeing madebetween the tip of the plug "Pand the sleeve ofthejacket while theplug'is being insertedinto-the said jack. Ground ispresenton the tip of the plug P being supplied :by the winding oftheback 229 and its front contact, off normal springs 231 and 230throughthe Winding of the vertical magnet 219 and then'through the winding oftheslow acting relay 213 to battery. The above is'the circuit over whichthe first impulse to the vertical magnet is transmitted. Upon the firstvertical step of the shaft the off normal springs are shifted and theremaining vertical magnet impulses are sent over a circuit whichisadifierent from the one reviously traced'inasmuch as it includes theoff normal springs 23land 232 and armature 236 and itsfrontcontact,:relay 213 being new in an operated position. Magnet 219operates to 'raise the switch wipers258-261, inclusive, step bystep-until they. are placed opposite the leve'lofbank contacts in whichis located the terminals of the substation A. The slow aot ing relay 213which is energized in series with the vertical magnet maintains itsarmature attracted throughout the vertical movement of the switch and-atits termination retracts its armatures and'transfers the impulsingcircuitrto the rotary magnet 220.

The private automatic exchange operator may now-operate her callingdevice in accordance .with the final digit of the called subscribersnumber As before, a series of interruptions is produced in the circuitof line relay 210 which deenergizes a plurality oftimes in'responsethereto. Upon each deenergization, a circuit is completed extending fromground by way of armature 226 and its back contact, armature 229 and itsfront contact, oifanormal springs-231 and 232, armature 286 and its backcontact, back contact and armature 246, through the winding of the slowacting low resistance relay 216, armature 256 and its back contact, andhence through the winding of the rotary magnet 220 to battery. Magnet220 operates to rotate .the wipers 258-261, inclusive, into engagementwith the bank cont-acts associated with the line of the desired calledsubstation A which .wewill assume are the bank contacts 216 is energizedin series with the rotary mag-- contact 264. A circuit may then betraced extending from the said grounded test contact by way of testwiper 260, armature 250 and its front contact and through the winding ofthe test relay 215 to battery. Relay 215 energizesover this circuit andoperates to establish a point in its locking circuit at armature 245,this being completed upon the deenergization of the slow acting relay216, at armature 246 opens the circuit of the rotary magnet, at armature247 prepares an automatic testing circuit which will be described laterand at armature 248 places a busy tone on the lower heavy talkingconductor 202. This tone will be audible to the attendant operator andthe calling subscriber and will serve to inform them that the desiredline is busy. Should the calling subscriber in the main exchange nowdesire a connection with another subscriber in the private automaticexchange he may inform the attendant of this fact. The attendantoperator will then operate the release key K therebyopening the circuitof the line relay 210 of the connector H. When this relay deenergizesthe slow acting release relay 211 deenergizes shortly after and thecondenser H is released in the well known manner. The operator may now,by operating her calling device for the digits of the desiredsubscribers number, cause the connector H to connect with the desiredlines. The operation in this case is similar to that just described andwill be readily apparent. However, should the calling subscriber in themain exchange replace his receiver upon hearing the audible busy signalthe connection will be released in a manner which will be describedhereinafter.

It will now be assumed that the line of the substation A is idle whenthe wipers of the connector H are rotated into engagement with the bankcontacts 262-265, inclusive. Under these conditions there will be noground on the test contact 264 and the test relay 215 is not operated.Then, following the deenergization of the slow acting relay 216, acircuit is completed extending from ground by way of front contact andarmature 228, normally closed springs controlled by.

armature 235, armature 245 and its back contact, through the lowerwinding of the switching relay 217, back contact and armature 250, testwiper 260, .test contact 264, through the winding of the switching relay266 and motor magnet 267 of the line switch C to battery;

The relays 217 and 266 operate over this circuit. However, due to amechanical interlocking device controlled by the armature of the linerelay 268 which has not been .en-

ergized, the switching relay 266 only attracts its armatures enough todisconnect the line of the substation A from its normal battery andground connections in the line switch C. v

In the connector H, the switching relay 217, upon energizing,establishes a locking circuit for itself at its armature 254, placesground upon the test wiper 260 at armature 255, opens the rotary magnetcircuit at armature 256 and at armatures 252 and 257 completes theringing circuit.

Having completed the desired connection the attendant operator may nowrestore the listening key K This operation disconnects her head set fromthe connection and enables her to attend to other calls. By therestoration of key K the circuit of the line relay 210 of the connectorH is transferred to ground through the springs 195 and armature 197 ofrelay 17 6 and its back contact for a purpose which will appearsubsequently.

In the connector H, ringing current is now intermittently applied to theline of the substation A until an answer is obtained. When this occurs acircuit is completed over the called subscribers line for the ring outoff relay 214. Upon energizing, this relay establishes a locking circuitfor itself at armature 238, at armatures 237 and 239 opens the ringingcircuit and at the front contact of these armaturesfinally completes thetalking connection.

When the ring cut off relay 214 energizes a direct metallic circuitextends from the back bridge relay of-the connector H in the mainexchange to the substation A. The current flowing over this circuitserves to energize the relay 179 in the cord circuit 0. Relay 179, uponenergizing, opens the circuit of the calledsupervisory lamp L therebynotifying the attendant operator that the called subscriber has answeredand closes the circuit of the slow acting relay 280 at armature 282.Upon operating relay 280 prepares a circuit for relay 176 at armature281. The conversation may now be carried on over the heavy talkingconductors between the subscriber in the main exchange and thesubscriber at substation A, battery being supplied to the subscriber inthe mainexchange from the windings of the line relay 16 of the connectorH and to the called subscriber at substation A in the private automaticexchange from the windings of the back bridge relay 15 of the connectorH.

At this point it will be convenient to describe the operation of-thelocal connector H when it operates to select an idle line in a group oflines. In order to arrange-the connector H. to give this class ofservice two test wipers are provided. In order to enable the switch todiscriminate between rivate and rotary busy lines the test contacts ofthe latter engaged by the two test wipers must be tied together andthose of the last trunk line in the group or those of private lines leftopen. Assuming that the connector His rotated into engagement with sucha group of lines and that the first line thereof is busy. Under theseconditions there will also be a ground potential on the test contactengaged by the test wiper 259 as well as the test wiper 260. A circuitis now completed extending from the grounded test contact engaged by thetest wiper. 259, over said test wiper, back contact and armature 249armature 253 and its back contact, back contact and armature 221,armature 247 and its front contact, through the winding of the steppingrelay 212 and thence through the winding of the slow acting relay 213 tobattery. Therelays 212 and 213 are energized over, this circuit. Relay213, upon energizing, again connects the test-wiper 260 to the testrelay 215 at armature 235. Relay 212, upon energizing, establishesalocking circuit for itself and relay 213 at armature 233 and atarmature 234 completes the circuit of the rotary magnet 220. Magnet 220'operates to rotate the switch wipers 258-261, inclusive, into engagementwith the next set of bank contacts in the selected group, and atarmature 221 opens the locking circuit of the relays 212 and 213. Upondeenergizing, relay 212 opens a circuit of the rotary magnet 220 whichdeenergizes also. If this next trunk line is not the last one of thegroup and is busy the test relay 215 will be maintained energized andthe stepping relay 212 will operate as before. The alternate operationof the stepping relay 212 and the magnet 220 continues until an idleline is found or until theswitch wipers are rotated into associationwith the last trunk line of the group. If this is busy also test relay215 will be maintained energized. However, no circuit will be completedfor the stepping relay 212 and as ground is not present on the testcontact engaged by the upper test wiper 259 the rotation of the switchceases and a busy tone is given to the calling subscriber. In case theconnector H is rotated into engagement with an idle trunk line theoperation proceeds as before described.

Referring back to the description of the extension of the connection,when the conversation is terminated both the subscribers will replacetheir receivers upon their respective switch hooks. In order to describethe releasing operation in detail it will be assumed that the calledsubscriber at substation A replaces his receiver before the callingsubscrib er in the main exchange. When the receiver is replaced atsubstation A the circuit of the supervisory relay 179 in the operatorscord circuit 0 is opened and this relay deenergizes. Upon retracting itsarmatures, a circuit is closed for the lamp L in order to notify theoperator that the called subscriber has replaced his receiver and atarmature 282'the circuit of the slow acting relay 280 is opened andbefore the deenergization of this latter relay an impulse of current issent, over a path extending from groundbyway of the said armature andits back contact, armature 281 and its front contact. and through theWinding of relay 176 to battery. Relay 176, upon operating, at itsarmature 181 discon nects ground from the sleeve of the plug P, at thefront cont-act of this armature establishes an auxiliary circuit for thesleeverestores the normal flow of current over the conductors 10 and 12of the incoming trunk line and at armature 32 opens the circuit of theslow acting relay 33. After the deenergization of relay 15 and beforethe deenergization of relay 33 an impulse of current is sent over acircuit extending from ground by way of armature 32 and its backcontact, front contact and armature 34, and through the winding of therelay 25 to battery. A circuit in multiple with the above is completedfor the slow acting relay 29. Theoperation of relay 29vat this timeserves merely to remove one ground connection from therelease trunkconductor 11. Upon energizing, relay 25 at its armature 59 establishes alocking circuit for itself and relay 29cto ground on conductor 51 and atarmature 284 opens the circuit of the slow acting relay 17, Theoperation of the other armatures of relay 25 are without function at thepresent time. Upon the deenergization of the slow, acting relay 17ground is removed from the release trunk conductor 11 thereby opening aholding circuit of the previously operated switches in. the mainexchange and the circuit of the release magnet 102 of the connector H isprepared. Immediately upon the deenergization of the relay 25 whichtakes place as soon as its locking circuit is opened by the deenergization of the slow acting relay 17 magnet 102 operates to restore theconnector H to its normal position in the usual manner.

' Returning now to the description of the circuit operations in theprivate automatic exchange the results occasioned by the disconnectionof ground from the sleeve of the plug P will now be considered. Whenground is disconnected from the sleeve of plug P the circuit of therelay 151 in the trunk equipment is opened as is the circu t of thevisual 168. Relay 151, upon deenergizing, at its armature 164 againbridges the lower winding of the ring up relay 150 and the windings ofthe high resistance polarized relay 152 across the trunk conductors 140and 141. It will be understood that when the connector H in the mainexchange was released that the cut off relay 121 in the line switch C isdeenergized to a ain connect the normal battery to the truni conductors140 and 141. As this battery flows in the opposite direction to thatsupplied by the connector H the polarized re- I lay 152 in the trunkcircuit at the'private automatic exchange is energized. Upon attractingits armature, relay 152 opens the circuit of the slow acting relay 153.Upon deenergizing, the'latter relay removes ground from the releasetrunk conductor 170 associated 2 with the multiples of the'incomingtrunk line. comprising conductors 140 and 141 in the banks of the localconnector switches. The two way trunk line shown in the drawings may nowbe used for a call in either direction even though relay 211. '-Uponretracting its-armatures,

the latter relay opens certain locking circuits in the connector H andcloses the circuit of the release magnet 218. The release magnet 218operates to release the connector inthe usual manner.

The private automatic exchange operator upon noting the lighting of thelamp L will withdraw the plugs of the cord circuit from their associatedjacks. Upon the plug P reaching its normal position the lockingcirthereby cuit of the relay 17 6 is opened and this relay deenergizesto open the circuit of the relay 175 and restore certain other circuitsin the cord circuit to normal.

Adverting back to the description of the extended connection it will beassumed that the calling subscriber in the main exchange is the first toreplace his receiver.- When the receiver is replaced at the callingsubsta- 16 in the connector H is opened. This relay deenergizes and inturn opens the circuit of the slowacting release relay 17. Uponretracting its armatures the latter relay removes ound from the releasetrunk conductor 11 release, at armature 37 opens the locking circuit ofthe various relays in the connector H and at armature 39 completes thecircuit of the release magnet 102. Magnet 102 operates to restore theconnector H to normal. As soon as ground is removed from the testcontact 107 associated with thetrunk line comprising conductors 140 and141, the cut oif relay 121 in the line switch C retracts its armaturesthereby again'connecting the norallowing the preceding switches to malbattery to the trunk line. This battery flows in the opposite directionto that which has'been supplied by the connector H. Current is nowreversed in the'lower winding of the electro-polarized relay 17 7 andthis relay retracts its armatures. Upon so doing, relay 17 7 at armature186 establishes the circuit of the supervisory lamp L which notifies theattendant that the calling subscriber has replaced his receiver and atarmature 187 opens the circuit of the slow actingrelay 178. After thedeenergization of the polarized relay 177 and before the deenergizationof the slow actmg relay 178 an impulse of current is sent over a circuitextending from ground by way of armature 187 and its back contact, frontcontact and armature 188 and through the winding of the relay 176 tobattery. Relay 176 operates in the same manner as before to establish alocking circuit for itself at armature 182, to open at armature 197 thecircuit of the line relay 210 of the connector H, to open at armature181 the circuit of the busy visual 168 associated with thetrunk circuitand also that of relay 151 and at the front contact of this armature toestablish another circuit for the sleeve relay 17 5. Another re sult ofthe energization of relay 17 6 is that at armatures 183 and 184 the cordcircuit is disconnected from the trunk even though the plug P remains inthe jack J. As the circuit of the line relay 2100f the incomingconnector H is opened the release of the connector H takes place asbefore described. As the circuit of the relay 151 in the trunk equipmentassociated with the jack J is also opened by the operation of relay 17 6this relay will deenergize to again connect the lower winding of thering up relay and the windings of the high resistance polarized relay152 across the trunk conductors 140 and 141. The polarized relay 152 isimmediately energized and operates to open the circuit of the slowacting relay 153. The latter relay deenergizes after a short'intervaland again renders the multiples of the trunk line accessible in thelocal connector switches by removing ground from the release trunkconductor 170. The trunk line comprising conductors 140 and 141 is nowfree and may be used for calls in either direction even though the plugP remains in the jack J and the ordinary supervisory call signaloperates just the same as if the plug P were out of the jack.

' In response'to the lighting of the supervisory lamps L and L theoperator will withdraw the plugs of the cord circuit from the jacks Jand J as beforedescribed. When the plug P reaches its normal positionthe plug seat switch PS is operated and the looking circuit of the relay17 6 is opened. Upon deenergizing, this relay opens the circuit of thesleeve relay 175 and restores certain other circuits to normal. However,should the attendant be busy and leave the plug in the jack for sometime after the operation of the supervisory signals the trunk linecomprising conductors 140 and 141 may still be used for calls in eitherdirection as has already been indicated. The operation under theseconditions will now be described.

If the trunk line is again seized in the main exchange the polarizedrelay 152 is energized to busy the trunk line to the local switches inthe private automatic exchange and the ringing current impressed uponthe trunk line op erates the ring up relay in the same manner as before.Relay 150 locks itself energized and closes the circuit of thesupervisory lamp L. Under these conditions the operator has only tooperate the listening key K in order to answer the call. By thisoperation the cord circuit is associated with the trunk as the'lockingcircuit of the relay 176 is opened and all circuits are now in the samecondition as if the operator had answered the call by plugging into thejack.

Should the trunk line be seized for an outgoing call from the privateautomatic to the main exchange ground will be placed upon the conductorby the local connector selector repeater-thereby energizing the relay151 of the trunk circuit in multiple with the busy visual 168. Theoperation of the visual 168 serves to notify the operator that the trunkline is being used for an outgoing call. Relay 151 operates to removethe lower winding of the ring up relay 150 and the high resistancepolarized relay 152 from bridge of the two trunk conductors 140 and 141.The line relay 123 of the line switch C associated with the seized trunkline in the main exchange is immediately energized via a direct currentbridge in the connector selector repeater and operates to close thecircuit of the switching relay 121 in series with the motor magnet 125.It will be noted that the test wiper 143 is normally connected through aback contact on switching relay 121 to a point in the above circuitmidway between the switching relay and the motor magnet. Thus it will beseen that as soon as the trunk line with which the switch wipers of theline switch C are associated becomes busy the ground potential on thetest contact engaged by test wiper 143 causesthe operation of the motormagnet 125. Thus it will be seen that the wipers of the line switch arealways associated with an idle trunk line or else are being operated insearch of one. That is, the rotary line switch C preselects its trunks.

Returning now to the operation of the line switch C when the trunk linecomprising conductors 140 and 141 was seized in the private automaticexchange the line relay 123 energizes as before described and closes thecircuit of the switching relay 121. The latter relay, upon operating,extends the seized trunk conductors to the line relay of the selctedfirst selector at armatures 126 and 129, at armature 127 opens a pointin the circuit of relay 124 and at armature 128 prepares a holdingcircuit for itself. subsequentoperations wherein the connection isextended to the desired called line in response to the digits dialled bythe calling subscriber in the private automatic exchange takes place inthe usual manner.

The attendant operator sometimes finds it desirable to extendconnections to the main exchange for certain subscribers in theprivateautomatic exchange. In order to enable her to do this when theplug of av cord circuit is placed in the jack of an idle trunk line acalling out keysuch as key K in the cord circuit 0 is provided in allthe cord circuits. The operation will now be briefly described when theoperator desires to extend a call to a subscriber in the main exchange.When the operator inserts the plug of an idle cord circuit into the jackof an idle trunk line, the plug P into the jack J for example, a circuitis completed for the relay 151 over the sleeve of a cord circuit inmultiple with the visual 168. Relay 151 operates to remove the ring uprelay 150 and the high resistance polarized relay 152 from bridge of thetrunk conductors 140 and 141 as before described. Relay'152 immediatelyretracts its armature as its circuit is now open. However, its operationis ineifectiveat the present time to close a circuit of the slow actingrelay 153. The multiples of the trunk line comprising conductors 140 and141 in the banks of the local connector switches are busied by groundthrough the winding of the low resistance relay over a circuit extendingfrom ground through the winding of relay 175, normally closed springscontrolled by armature 181, sleeve of plug P, sleeve of jack J, backcontact and armature 167 to release trunk conductor 170. If the operatorplugs into the jack with the key K thrown the calling device CD isbridged 1 across the conductors 140 and 141. This occurs in thefollowing manner: When the key K is operated the relay is energ zed.Upon operating, this relay at its armature The 191 bridges the callingdevice across the I trunk circuit over the circuit extending fromconductor 140, tip of plug P, working contact of spring 197 and the saidspring, springs of release key K impulse springs of the calling deviceCD, front contact and armature 191, right hand winding of the repeatingcoil associated with the operators head set, spring 149 of key K and itsworking contact, ring of plug P, ring of jack J, to trunk conductor 141.Line relay 123 is immediately energized over this circuit and the lineswitch C operates to extend the connection to a preselected firstselector switch. Should the operator plug in the jack J with the key Knormal the line relay 123 of the scriber in the main exchange to hold tline freed for use as line switch C would be energized in series withthe lower Winding of electropolarizmg relay 177 of the cord circuit 0.However,

the polarized relay would not be operated at this time as the current inits polarizing win-ding opposes the current in its other winding, itbeing of course understood that when the plug P was placed in the jack Jrelay 175 operated to energize the polarized winding of relay 177 and tolight the supervisory lamps L and L In response to the digits dialled bythe attendant operator in the private automatic exchange a series ofautomatic switches in the main exchange are operated to extend theconnection to the desired called subscribers line in a Well knownmanner. When the connection is completed the attendant operator willrestore the key K to normal. When the called subscriber answers thenormal current flow is reversed over the trunk conductors 140 and 141and the electropolarized relay 177 in the cord circuit 0 is operated toefface the supervisory lamp L thereby notifying the attendant that thecalled subscriber has answered. The attendant operator will now throwthe key K and inform the called subhe line. She will then set up theconnection to the party in the private automatic exchange who has askedher to' establish the connection. The operation in the establishment ofa local connection has already been described and will be readilyunderstood. When the subscriber in the private automatic exchangeanswers the attendant is informed of this fact by the efl'acement of thesupervisory lamp L which occurs upon the energization of the relay 179.If the subscriber in the private automatic exchange replaces hisreceiver before the called subscriber in the main oflice, the relay 179is deenergized, the supervisory lamp L lighted, the local incomingconnector such as H released. and the trunk before described. Should thecalled subscriber in the main exchange be the first to replace hisreceiver the normal current flow is again restored over the trunk linecomprising conductors 140 and 141 and the electropolarized relay 177will be deenergized thereby lighting the supervisory lamp L to notifythe operator that the called subscriber has replaced his receiver andopening the circuit of the slow acting relay 178 and closing the circuitof the relay 176. As before, relay 176 operates to establish a lockingcircuit for itself, to remove ground from the sleeve of the jack J andto disassociate the cord circuit from the trunk line. As there is now nobridge across the trunk conductors 140 and 141 the operated switches inthe main exchange are released in the usual manner and the two way trunkline is rendered accessible for calls in either direction in the samemanner as before described. Another circuit is opened.Upondeenergizing,.this

relay opens the circuit of the sleeve relay 17 5 and restores certainother circuits in the cord circuit to normal.

It will now be convenient to describe certain features of the trunkcircuit comprising conductors 140 and 141 interconnecting the main andbranch exchanges whereby if the trunk line becomes either open orgrounded it is automatically made busy at both ends and an alarm signalgiven to the exchange attendant in the main exchange. It will be notedthat the energizing circuit for the high resistance polarized relay 152includes the line relay 123 of the line switch C associated with thetrunk line in the main exchange and also the rightand left hand windingsof the shunt field relay 122. The construction of the relay 122 issimilar to that of the relay 21 in the connector H already described.The relays 122 and 152 are energized over this circuit. However the linerelay 123 remains inoperative due to the high resistance of thepolarized relay 152 and the shunting eifect of the relay 122. Now shouldthe trunk circuit become opened relays. 122 and 152 will denergize.Relay, 152 upon deenergizing, closes the circuit of the slow actingrelay 153. The latter relay operates to place a busy potential upon themultiples of the trunk line in the banks of the local connector switchesthereby preventing it being seized by a subscriber in the privateautomatic exchange. Relay 122 upon deenergizing opens the circuit ofline relay 123 at its armature 145, and its armature 130 closes thecircuit for the lower winding of the relay 124. It will be seen that therelay 124 is slow to energize but quick to deenergize as its upperwinding isnormally short circuited by armature 138 and its back contact.After a short interval relay 124 energizes and, upon operating.establishes a locking circuit for itself at armature 133 to ground oncommon conductor 148, places ground upon the multiple test contacts suchas 107 in the banks of the rotary connector switches and at armature 132closes the circuit for an alarm in series with the lamp L? to notify theattendant that one of the interconnecting trunk lines is in trouble. Thelamp L is individual to the trunk lines extending to one privateautomatic exchange and serves to inform the attendant in what group oftrunk lines to look for the trouble. When ground is placed on theconductor 120 the relay 121 is energized and operates to disconnectnormal battery and ground and the windings of relay 122 from the trunkline conductors 140 and 141 for a purpose which will subsequently bemade clear. When the trouble is cleared the attendant will operate thecommon key K which opens the locking circuit of the relay 124. Upondeenergizing, relay 124 removes ground from the multiple test contactsin the banks of the rotary connector switches. As the trunk line is nowin good condition the relay 122 will now be energized to preparethecircuit of the line relay 123 and to open the circuit of the relay124. If the trunk line should become grounded on either conductor theleft hand coil of the relay 122 will be short circuited and this relaywill be 'deenergized thereby opening a circuit of the line relay 123 sothat it does not energize at this time at armature 145 and at armature130v completes the circuit for the slow to operate relay 124. Sincerelay 122 is disconnected from both trunk conductors 140 and 141, in themanner previously described, current flow to the polarized relay 152 iscut oil? regardless of which trunk conductor is grounded and this relaytherefore deenergizes to busy the trunk line to the local connectorswitches in the private branch exchange in the same manner as if thetrunk were open. Otherwise the operations are the same as have alreadybeen described.

Returning now to the connector H it will be remembered that when theconnector switch automatically rotated until its wipers were associatedwith the last trunk line of the group and, if this trunk line is idle,the relay 20 energized. This relay operated to reverse the connectionsof the ring out off and back bridge relay with respect to the switchwipers. The reason for this will now become apparent, inasmuch as thenormal conductors extending from the line switch to the connector banksin the case of the last lines in a group are not reversed as in rotarylines therefore the wipers of the connector switch must be connected inthe opposite manner so as to properly operate the polarized relay 152 inthe trunk circuits at I, the branch exchanges and the electropolarizedrelay 177 in the cord circuit. By the operation ofrelay 20 this resultis secured the same as if the normal conductors extending from the lineswitch to the normal connector banks are reversed.

The features of the invention having been fully described what isconsidered to be new and desired to have protected by Letters Patentwill be pointed out in the appended claims.

What I claim as my invention is: I

1. In a telephone system, a two way trunk line interconnecting twoexchanges, automatic switches in each exchange having access to saidtrunk line and means operative automatically responsive to said trunkline becoming open for rendering it inaccessible to said automaticswitches in both exchanges.

2. In a telephone system, a two way trunk line interconnecting twoexchanges, automatic switches in each exchange having ac-.

cess to said trunk line and means operative automatically responsive tosaid trunk line becoming grounded for rendering it inaccessible to saidautomatic switches in both exchanges.

3. In a telephone system, a two Way trunk line interconnecting twoexchanges, automatic switches in each exchangev having access to saidtrunk line andvmeans operative automatically responsive to said trunkline becoming open for signalling an attendant at one of said exchanges.

4. In a telephone system, a two way trunk line interconnecting twoexchanges, automatic switches in each exchange having access to saidtrunk line and means operative automatically responsive to said trunkline becoming grounded for signalling an attend ant at one of saidexchanges.

5. In a telephone system, a two way trunk line interconnecting twoexchanges, automatic switches in each exchange having access to saidtrunk line and means operative automatically responsive to said trunkline becoming open or grounded for rendering it inaccessible toautomatic switches in both exchanges. I

6. In a telephonesystem, a two way trunk line interconnecting twoexchanges, automatic switches in each exchange having access to saidtrunk line and means operative automatically responsive to said trunkline becoming open or grounded for signalling an attendant at one ofsaid exchanges.

7. In a telephone system, a two way trunk line, automatic switcheshaving access to each end of said trunk line, and means operativeautomatically responsive to said trunk becoming open for rendering itinaccessible to said automatic switches.

8. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means in said cordcircuit operative when said calling line is disconnected from said trunkline for disconnecting the called line from said cord circuit.

9. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means controlled fromsaid calling line for disconnecting said called line from said cordcircuit.

10. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means including arelay controlled from said calling line for disconnecting said calledline from said cord circuit.

11. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means controlled fromsaid called line for disconnecting said called and calling lines fromsaidtrunk line.

12. In a telephone system, a trunk line, a calling line, automaticswitches controlled from said calling line for seizing said trunk line,an operators cord circuit for connecting said trunk line to a calledline, and means controlled from said called line independent of saidcalling line for disconnecting said cord circuit from said called line.

13. In a telephone system, a trunk line, a calling line, automaticswitches controlled from said calling line for seizing said trunk line,an operators cord circuit for connecting said trunk line to a calledline, and means controlled from said calling line for disconnecting saidcalled line from said cord circuit.

14=. In a telephone system, a calling line, a trunk line, automaticswitches controlled from said calling line for connecting with saidtrunk line, means including an operators cord circuit and automaticswitches for connecting said trunk line with a called line, and meanscontrolled from said called line for releasing all of said automaticswitches used in said connection.

15. In a' telephone system, a calling line, a trunk line, automaticswitches controlled from said calling line for connecting with saidtrunk line, means including an operators cord circuit and automaticswitches for connecting said trunk line with a called line, and meanscontrolled from'said calling line for releasing all the automaticswitches used in said connection;

16. In a telephone system, a calling line, a trunk line, automaticswitches controlled from said calling line for connecting with saidtrunk line', means including an operators cord circuit and automaticswitches for connecting said trunk line with a called line, meanscontrolled from said called line for releasing all said automaticswitches used in said connection, and means controlled by the release ofsaid switches for rendering said trunk line accessible to be used foranother call even though said cord circuit remains associated with saidtrunk line.

.17. In a telephone system, a calling .line, a trunk line, automaticswitches controlled from said calling line for connecting with saidtrunk line, an operators cord circuit for connecting said'trunk line toa called line, a disconnect signal at said cord circuit, circuitconnections controlled by the release of said all automatic switcheswhen the calling line is disconnected for reversing the flow of currentover said trunk line and a relay in said cord circuit responsive to saidcurrent reversal to control said signal. i

18. In a telephone system, a calling line, a trunk line, automaticswitches controlled from said calling line for connecting with saidtrunk line, an operators cord circuit for connecting said trunk line toa called line, a signalling circuit, circuit connections for re leasingsaid automatic switches and for reversing the flow of current over saidtrunk line when the receiver is replaced at the called substation and arelay in said cord circuit responsive to said current reversal tocontrol said signal. I

In a telephone system, a calling line, a trunk line, an operatorsposition, automatic switches controlled from said calling line forconnecting with said trunk line, a signal at said operators positionresponsive to such connection, a cord circuit atsaid position forconnecting said trunk line to a called line, means controlled from saidcalled line for releasing said automatic switches to render said trunkline accessible to other calls, and means operative when said trunk lineis again seized even though said cord circuit remains associated withsaid trunk line for operating said signal. V

20. In a'telephone system, a trunk line terminating in an automaticswitch, other automatic switches accessible thereto, an operatorsposition, means controlled by the operator at said position for seizingsaid trunk line and. for operating the first mentioned switch and aseries of said other switches to extend a connection to a called line,means controlled only by said operator for releasing said switches, acalling line, means controlled from said calling line for seizing saidtrunk line and for operating said first mentionedlswitch and a series ofsaid other switches to extend aconnection to another called line, andmeans controlled from said other called line for releasing saidconnection.

21. In a telephone system, a trunk line terminating in an automaticswitch, other automatic switches accessible thereto, an operatorsposition, means controlled by the operator at said position for seizingsaid trunk line and for operating thefirst mentioned switch and a seriesof said other switches to extend a connection to a called line, meansextend a connection to said called line, and means controlled from saidcalled line for releasing said connection.

22. In a telephone system, a trunk line terminating in an automaticswitch, other automatic switches accessible thereto, an opera-torsposition, means controlled by the operator at said position for seizingsaid trunk line and for operating the first mentioned switch and aseries of said other switches to extend a connection to a called line,means controlled only by said operator for releasing said switches, acalling line,

means controlled from said calling line for seizing said trunk line andfor operating said first mentioned switch and a series of said otherswitches to extend a connection to another called line, and meanscontrolled from either the calling or said other called line for relay.

25. In a plug ending cord circuit for connecting two lines, a relay foropening the talking circuit through said cord circuit, means responsiveto the replacement of the receiver on one of the connected lines fortransmitting a momentary impulse to energize said relay, and a lockingcircuit for holding said relay energized.

26. In a plug ending cord circuit for connecting two lines, a relay foropening the talking circuit through said cord circuit,

means responsive to the replacement of the receiver on one of theconnected lines for transmitting a momentary impulse to energize saidrelay, a locking circuit for holding said relay energized, and meansresponsive to the manual restoration of the cord to normal for openingsaid locking circuit.

27. In a plug ending cord circuit for connecting two lines in which eachplug has a sleeve contact in addition to the two talking contacts, saidcord circuit comprising circuit arrangements whereby electricalpotentials are maintained on said sleeve contacts while the cord circuitis in use, a relay for removing said potentials, and means responsive tothe replacement of the receiver on either connected line for energizingsaid relay.

28. In a plug ending cord circuit for connecting two lines in which eachplug has a sleeve contact in addition to the two talking contacts, saidcord circuit comprising circuit arrangements whereby electricalpotentials are maintained on said sleeve contacts while the cord circuitis in use, a. relay for removing said potentials, and means responsiveto the replacement of the receiver on one of the connected lines forenergizing said relay.

29. In a plug ending cord circuit for connecting two lines in which eachplug has a sleeve contact in addition to the two talking contacts, saidcord circuit comprising circuit arrangements whereby electricalpotentials aremaintained on said sleeve contacts while the cord circuitis in use, a relay for removing said potentials, means responsive to thereplacement of the receiver on one of the connected lines fortransmitting a momentary impulse to energize said relay, and a lockingcircuit for holding said relay energized.

30. In a plug ending cord circuit for connecting two lines in which eachplug has a sleeve contact in addition to the two talking contacts, saidcord circuit comprising circuit arrangements whereby electricalpotentials are maintained on said sleeve contacts while the cord circuitis in use, a relay for removing said potentials, means responsive to thereplacement of the receiver on one of the connected'lines fortransmitting a momentary impulse to energize said relay, a lockingcircuit for holding said relay energized, and means responsive to themanual restoration of the cord to normal for opening said lockingcircuit.

31. In a telephone system, means including a cord circuitfor'connectingtwo lines, means outside the said cord circuit for supplying talkingcurrent to the connected lines, the talking current to the called lineflowing over the two strands of said cord circuit in series, meanscontrolled by the calling party for reversing the direction of the flowof talking current to the called line, and means in said cord circuitresponsive to the said reversal for opening the talking. circuit at saidcord circuit.

32. In a telephone system, means including a cord circuit for connectingtwo lines, means outside the said cord circuit for supplying talkingcurrent to the connected lines, the talking current to the called lineflowing over the two strands of said cord circuit in series, meanscontrolled by the calling party for reversing the direction of the flowof talking current to the called line, means in said cord circuit formaintaining both connected lines in busy condition, and means in saidcord circuit responsive to said reversal for rendering said busy meansineffective. 38. In. a telephone system, means including a cord circuitfor connecting two lines, means outside the said cord circuit forsupplying talking current to the connected lines, the talking current tothe called line flowing over i the two strands of said cord circuit inseries,

means controlled by the calling party for reversing the direction of theflow of talking current to the called line, and means in said cordcircuit responsive to the said reversal for opening the talking circuitat said cord circuit, said last means including a polarized relaybridged across the talking strands of said cord circuit.

34. In a telephone system, means including a cord circuit for connectingtwo lines, means outside the said cord circuit for supplying talkingcurrent to the connected lines, the talking current to the called lineflowing over the two strands of said cord circuit in series, meanscontrolled by the calling party for reversing the direction of the flowof talking current to the called line, means in said cord circuit formaintaining both connected lines in busy condition, and means in saidcord circuit responsive to said reversal for rendering said busyingmeans ineffective, said lastmeans including a polarized relay bridgedacross the talking strands of said cord circuit.

In a telephone system, a cord circuit for connecting two lines, means insaid cord circuit for maintaining certain potentials on the jacks of theconnected lines to make them busy, a relay in said cord circuit throughwhich talking current is supplied to one of the connected lines from apoint in the talking connection between the cord circuit and the otherconnected line, and means responsive to the deenergization of said relayfor removing said busy potentials.

36. In atelephone system, a cord circuit for connecting two lines, meansin said cord circuit for maintaining certain potentials on the jacks ofthe connected lines to make them busy, a relay in said cord circuitthrough which talking current is supplied to one of the connected linesfrom a point in the talking connection between the cord circuit and theother connected line, and means responsive to the deenergization of saidrelay for removing said busy potentials and for opening the talkingstrands of said cord circuit.

37 In a telephone system, a main exchange, a branch exchange, a trunkline connecting said exchanges, means including-said trunk line and aseries of automatic switches in the main exchange for extending a callfrom a calling party in the main exchange to the branch exchange, a plugending cord circuit in the branch exchange, means including said cordcircuit and a local trunk line and automatic switch in the branchexchange for completing the connection to the called line, and meansunder the control of either the calling or called party for releassaidtrunk line anda series of automatic switches in the main exchange forextending a call from a calling party in the mam exchange to the branchexchange, a plug ending cord circuit in the branch exchange, meansincluding said cord circuit and a local trunk line and an automaticswitch in the branch exchange for completing the connection to thecalled line, and means under the control of either the calling or calledparty for opening the talking circuit at said cord circuit.

- 39. In a telephone system, a main exchange, a branch exchange, a trunkline connecting said exchanges, means including said trunk line and aseries of automatic switches in the main exchange for extending a callfrom a calling party in the mainexcha'nge to the branch exchange, a plugending cord circuit in the branch exchange, means including said cordcircuit and a local trunk line 1 and an automatic switch in the branchexchange for completing the connection to the called line, and meansunder the control of either the calling or called party for opening thetalking circuit at said cord circuit and for restoring all of saidswitches to normal.

40. In a telephone system, a main exchange, a branch exchange, a trunkline connecting said exchanges, means including said trunk line and aseries of automatic switches in the main exchange for extending a callfrom a calling party in the main exchange to the branch exchange, a plugending cord circuit in the branch exchange, means including said cordcircuit and a local trunk line and an automatic switch in the branchexchange for completing the connection to the called line, and meansunder the control of the calling party for releasing all said switches.

41. In a telephone system, a main exchange, a branch exchange, a trunkline connecting said exchanges, means including said trunk line and aseries of automatic switches in the main exchange for extending a callfrom a calling party in the main exchange to the branch exchange, a plugending cord circuit in the branch exchange, means including said cordcircuit and a local trunk line and an automatic switch in thebranchexchange for completing the connection to the. called line, means forsupplying talking current to the called line from the main exchange, andmeans under the control of either the calling or called party forreleasing all said switches.

42. In a telephone system, a main exchange, a branch exchange, a trunkline connecting said exchanges, means including said trunk line and aseries of automatic switches in the main exchange for extending a callfrom a calling party in the main exchange to the branch exchange, a plugending cord circuit in the branch exchange, means including said cordcircuit and a local trunk line and an automatic switch in the branchexchange, for completing the connection to the called line, means forsupplying talking current to the called line from the main ex change,and means under the control of the called party for opening the talkingcircuit atsaid cord circuit.

43. In a telephone system, a .main exchange, a branch exchange, a trunkline connecting said exchanges, means including said trunk line and aseries of automatic switches in the main exchange for extending a callfrom a callingpartyin the main exchange to the branch exchange, a plugending cord circuit in the branch exchange, means including said cordcircuit and a local trunk line and'an automatic switch in thebranchexchange for completingthe connection to the called line, means forsupplying talking current to the called'line from the main exchange, andmeansunder the control of the calling party for opening the talkingcircuit at said cord circuit.

44. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means in said cordcircuit operative responsive to the hanging up of the receiver of thecalling line for disconnecting the calling and called lines from saidcord circuit.

45. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line,

with a called line, and means controlled from said called lineindependent of said calling line for disconnecting said called line fromsaid cord circuit.

46. In a telephone system, a trunk line, means for connecting a callingline with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means controlled fromsaid called line for disconnecting said calling and called lines fromsaid cord circuit.

47. In a telephone system, a cord circuit for connecting two lines,means included in said cord circuit for maintaining both connected linesin busy condition, and means including a relay in said cord circuitcontrolled from one of said lines by current supplied to the talkingconnection at a point outside said cord circuit for removing the busycondition even though said cord circuit has not been disconnected.

48. In a telephone system, a cord circuit for connecting two lines,means included in said cord circuit for maintaining both connected linesin busy condition, and means included in said cord circuit controlledfrom either one of said lines for removing the busy condition. eventhough said cord circuit has not been disconnected.

49. In a telephone system, a calling and a called line, a cordcircuit,means for extending said calling .line to said cord circuit, a

50. In a telephone system, a calling and a called line, a cord circuit,means for extending said calling line to said cord circuit, a jackadapted when connected to said cord circuit to extend the calling lineto said called line, means included in said cord circuit for maintainingsaid calling and called lines in busy condition, and means included insaid cord circuit controlled from either said calling line ,or saidcalled line for removing said busy condition even though said jackremains connected with said cord circuit.

51. In a telephone system, a calling and a called line, a cord circuit,means for extending said calling line to said cord circuit, a jackadapted when connected to said cord cir cuit to extend the calling lineto said called line, means included in said cord circuit for maintainingsaid calling and called lines in busy condition, and means included insaid cord circuit controlled from said called line for removing saidbusy condition even though said jack remains connected with said cordcircuit. i

52. In a telephone system, a calling and a called line, a cord circuit,means for extending said calling line to said cord circuit, a jackadapted when connected to said cord circuit to extend the calling lineto said called line, means included in said cord circuit for maintainingsaid calling line in busy condition, and means included in said cordcircuit controlled from said called line for removing said busycondition even though said jack remains connected with said cordcircuit.

53. In a telephone system, a calling and a called line, a cord circuit,means for extending said calling line to said cord circuit, a jackadapted when connected to said cord circuit to extend the calling lineto said called line, means included in said cord circuit for maintainingsaid called line in busy condition, and means included in said cordcircuit controlled from either said calling line or said called line forremoving said busy condition, even though said'jack remains connectedwith said cord circuit.

54. In a telephone system, a trunk line and a signal therefor, meansfor-connecting a calling line with said trunk line and for operatingsaid signal, means including an operators cord circuit for connectingsaid trunk line

